Over many years there have been numerous proposals for power painting systems. Among these, for example, it has been suggested in U.S. Pat. No. 3,230,570 to employ a peristaltic pump. Such a pump provides the advantage that it facilitates cleaning after painting, or when changing color, since the paint passes through the pump inside a tube and does not come into contact with any other parts of the pump, only this tube requiring cleaning. However, there is the danger that this tube may rupture, or otherwise develop a leak, during use with consequential leakage of paint from the pump. Should such leakage go undetected, particularly if painting is being performed at a location rather remote from the pump, then considerable inconvenience could be caused by the leaking paint.